To install a pipe under a finished surface such as a driveway or street, for example, it is routine procedure to provide operating and target trenches on opposed sides thereof. The pipe or rod pusher device, replacing the bucket on a standard tractor-mounted hydraulic backhoe, is properly located in the operating trench by the boom mounted dipper stick of the backhoe. After the pusher device is properly positioned and braced for the pushing operation, a first rod length is manually inserted through a pair of drive jaws and drivingly engaged thereby to push said first rod length under the street or driveway. The trailing end of the first rod length is provided with a coupling to receive a second rod length whereupon the hydraulic drive means is reactivated to push the second rod forwardly toward the target trench. A sufficient plurality of rod length are similarly attached to preceeding rods until the leading tip end of the first rod length emerges into the target trench.
The leading tip end is threadably provided with a pusher cap which is then removed and replaced with an adaptor for attachment to the end of a pipe to be permenantly installed under the above surface; said pipe being so installed by reconditioning the bracing means and drive jaws to reverse the direction of movement to pull the pipe back through the hole formed by the rod until the leading end thereof, coupled to the rod, emerges into the operating trench.
The above described device and operation thereof is quite conventional, however, certain deficiencies and difficulties are encountered in the operation of the reversable drive jaws and replacement thereof when necessary because of wear.
To reverse the direction of drive, it is necessary to reverse the pitch or angle of inclination of each drive jaw relative to the push rod. Each jaw has an upper transverse rod, pivoted relative to the driven slide box, with a lever arm, fixed thereto as by welding. The jaw is held in either a forward or reverse drive attitude relative to the push rod by means of a tension spring extending between a fixed position to the slide box at a first end thereof, and a second end which is selectively attached to the shift lever either above or below the axis of the jaw pivot rod. Heretofore, to reverse the direction of drive, it has been necessary for an operator of the device to physically remove the second end of the tension spring from one end portion of the jaw lever and to reattach said second end relative to a second lever end portion.
The device of the present invention incorporates a slide bar, fixed relative to each jaw lever and extending above and below the axis of the jaw pivot rod. The second end of the tension spring is slidably engaged on the slide bar. When the lever is manually pivoted between the two drive positions, the second end of the tension spring will automatically slide along the slide bar to the slide bar end portion which is the closer to the fixed first spring end. This occurs because of the inherent tension forces of the spring.
It has been common practice to pivotally mount the jaw pivot rods through a pair of opposed side walls of the slide box assembly. Because of the wear factor on the gripping jaws, it is necessary to periodically replace said jaws. With the conventional structure it has been necessary to remove the entire slide box assembly from the device and to disassemble the slide box to remove the worn jaws for replacements. The slide box must then be completely reassembled and replaced in the device.
The pivot rods of the pair of drive jaws of the present invention are pivotally engaged in aligned pairs of top notches in the opposed side walls of the slide box and are pivotally maintained in place by a single, longitudinal, centrally disposed, removable keeper rod which is slidably engaged relative to the top of the slide box and said pivot rods. The keeper rod is normally maintained in position by a lock clip. To replace the drive jaws, the lock clip and keeper rod are removed with the slide box in place in the device. The worn drive jaws are lifted from the top slots and replaced by new jaws and the keeper rod and lock clip are replaced. Therefore, it can be seen that the complete jaw replacement operation can be accomplished in a matter of minutes whereas this operation has conventially been a long, laborious task.